The present invention relates to an aqueous recording liquid suitable either for an on-demand ink jet recording system, such as a piezoelectric system or a thermal system, or for a continuous injection type ink jet recording system such as a charge control system, and more particularly, to an aqueous recording liquid composition which exhibits excellent properties when used for printing on a plain paper and which can be also used as an aqueous recording liquid for a writing utensil, a recorder or a pen plotter.
In recent years, an ink jet recording system has been rapidly spreading because of its advantages such as compactness, low price, low running cost and low noise. An ink jet printer capable of printing on a non-coated plain paper such as a transfer paper for electrophotography, a printing paper, a typewriter paper, a wire dot printer paper, a word processor paper, a letter paper, a reporting paper is also placed on the market.
There have been proposed inks for use in such an ink jet printer having improved drying property to obtain an image of higher quality.
However, it is difficult to obtain an ink satisfying all the requirements; color reproducibility, water resistance, photoresistance, drying property, anti-blurring property and ejection reliability.
In the case of a color printer, even when no deterioration of image quality is observed in image areas printed in a single color of yellow, magenta or cyan, deterioration of image quality tends to occur in image areas of colors obtained by superimposing two color inks such as red, green and blue. In the case of a printer in which an image is dried without using a fixing unit, when the drying property of an ink is improved by enhancing the penetrability thereof as described in JP-A-S55-29546, the ink has a significant tendency to blur.
JP-B-S60-23793 suggests that, when dialkyl sulfosuccinate is used as a surfactant of an ink, the drying property of the ink can be improved without deteriorating image quality. However, the pixel diameter of a printed image remarkably varies depending upon the kind of a paper, and the density of the printed images is considerably decreased.
JP-A-S58-6752 discloses a quick drying ink whose anti-blur property is improved by enhancing the penetrability thereof using a surfactant containing an ethylene oxide having an acetylenic linkage.
However, some colorants cause the following problems. When an ink containing a direct dye such as DBK 168 is used, the drying rate of the ink cannot be improved due to a hydrophobic interaction between the surfactant and the colorant. When an ink containing a pigment such as carbon black is used, the pigment tends to aggregate, causing clogging of nozzles or inclination of ink ejection direction.
For the purpose of improving drying rate, JP-A-H8-113739 discloses an ink containing a dye and water-soluble glycol ethers and JP-A-H10-95941 proposes an ink composition composed of a pigment, glycol ethers such as diethyleneglycol mono-n-butyl ether and water.
However, a large amount of glycol ethers must be added to improve the drying rate of the ink, which is not preferable from the viewpoint of odor and safety.
JP-A-S56-57862 discloses an ink containing a strong basic substance. With this ink, an image with no deterioration can be formed on an acidic paper sized with rosin. However, this ink is not suitable for a paper prepared using alkyl ketene diner or alkenyl sulfosuccinic acid as a sizing agent. Even on an acidic paper, image deterioration is observed in image areas of colors obtained by superimposing two colors.
JP-A-138374 discloses an aqueous recording ink comprising a water-soluble dye, water and a benzyl ether having a specific structure. It is also suggested therein adding to the ink a vegetable oil, an unsaturated fatty acid, a higher alcohol, a fatty acid ester, an oily substance such as a mineral oil, and a hardly or slightly water-soluble solvent having a hydroxyl group in the molecular such as 2-ethyl-1,6-hexanediol, diethylene glycol hexyl ether, ethylene oxide adduct of acetylene glycol (having addition mole number of not greater than 5) and ethylene glycol benzyl ether for the purpose of further improving the penetrability of the ink. However, these inks have a problem in safety. Moreover, these inks have a significant problem in stability. The oily substance, the hardly or slightly water-soluble solvent benzyl ether and so on are separated at a certain environmental temperature.
Japanese Patent No. 2894568 proposes an ink jet ink comprising a composition containing a colorant and a liquid medium containing at least 60% by weight of water and 0.2 to 30% by weight of an alkylene glycol having 7 to 10 carbon atoms. Compounds shown as preferred examples of the alkylene glycol having 7 to 10 carbon atoms are 1,7-heptanediol, 2,6-heptanediol, 2,4-dimethyl-2,4-pentanediol, 3-ethyl-1,3-pentanediol and so on. It is said that, by addition of the compounds, there can be provided an ink which has xe2x80x9cimproved anti-blurring property, drying property and penetrability for a plain paperxe2x80x9d, which has xe2x80x9cgood balance between blurring property and penetrabilityxe2x80x9d and which is xe2x80x9chighly reliable in preventing clogging of ejection nozzlexe2x80x9d. In reality, however, the penetrability of the ink cannot sufficiently improved by addition of the above compounds and thus the drying property of the ink is still poor. Also, the ink is apt to blur on some types of papers. Namely, none of the problems of prior arts is not overcome.
Japanese Patent No. 2714482 proposes an ink jet ink containing an aliphatic diol compound having at least 6 carbon atoms and having a water solubility of at least 4.5% by weight at 25xc2x0 C. The diol compounds shown as the examples include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol, 5-hexene-1,2-diol, and so on. However, any inks containing the above compound cannot have sufficient penetrability and causes color bleeding or feathering.
JP-A-H6-157959 proposes an aqueous ink to which 2-ethyl-1,3-hexanediol is added for the purpose of improving permeability, and a recording method using the same.
2-Ethyl-1,3-hexanediol is not included in the examples of the usable compounds shown in Japanese Patent No. 2894568 but has been found to be able to be provide an aqueous ink composition which can satisfy the properties required of an ink jet ink, which is excellent in penetrability and drying property, and which can overcome the problem of image deterioration, and which can provide a recording method for producing a high-quality image using the ink composition. Since 2-ethyl-1,3-hexanediol can impart high ejection stability on high-frequency driving to an ink with a small amount, the method of recording using the ink is high in safety.
However, with the rapid progress of technologies in recent years, the printing speed of an ink jet printer has been greatly increased and it is not unthinkable that it will be much faster in the future. Under such circumstances, the ink is required to cause no color bleeding in printing at a higher speed and to dry quickly without transferring to a finger even if rubbed therewith immediately after printing.
In general, a quick drying ink has high penetrability. At the same time, a colorant in the ink is penetrated into a paper in the thickness direction thereof so largely that the image density tends to be decreased and strike-through is likely to occur. It is apparent that double-side printing will be essential with the progress of an ink jet printer and for the purpose of reducing paper consumption as an environmental issue. Thus, an aqueous ink having high drying property and causing so little strike-through as to permit double-side printing is demanded.
As has been described above, an aqueous ink jet ink which satisfies various requirements as an ink jet ink, which has high penetrability and drying property irrespective of the type of a colorant or the type of a paper, and which is capable of producing a high quality image with little strike-through is still required to be developed.
In recent years, a system for reading out recorded information printed with an ink which is invisible under ordinary circumstances with infrared rays or ultraviolet rays has been put to practical use in the fields of bar code printing and post mark printing. In view of preventing environmental pollution, application of an aqueous type recording liquid to such a system is under consideration. Additionally, in order to cope with such a system where high-speed processing is essential, an aqueous recording liquid having high penetrability is demanded.
The present invention has been made in view of the above problems and it is, therefore, an object of the present invention to provide a recording liquid which can overcome the drawbacks of the prior arts.
Another object of the present invention is to provide an ink jet recording method and an ink jet recording apparatus using the recording liquid.
In accomplishing the above objects, the present invention provides an aqueous recording liquid comprising a colorant, 2,2,4-trimethyl-1,3-pentanediol, and at least one surfactant selected from the group consisting of polyoxyethylene alkyl ethers and polyoxyethylene alkyl ether acetates.
In another aspect, the present invention provides a recording method for forming an image on a recording medium, comprising ejecting the above aqueous recording liquid as droplets onto said recording medium from a minute ejection nozzle.
The present invention further provides a recording liquid cartridge having a recording liquid container containing the above aqueous recording liquid.
The present invention further provides an ink jet recording device comprising the above recording liquid cartridge.